Evolution of the collective radiation dose of nuclear reactors from the 2nd through to the 3rd generation and 4th generation sodium-cooled fast reactors Joël Guidez, Anne Saturnin To cite this version: Joël Guidez, Anne Saturnin. Evolution of the collective radiation dose of nuclear reactors from the 2nd through to the 3rd generation and 4th generation sodium-cooled fast reactors. EPJ N - Nuclear Sciences & Technologies, EDP Sciences, 2017, 3, pp.32. 10.1051/epjn/2017024. cea-01794078 HAL Id: cea-01794078 https://hal-cea.archives-ouvertes.fr/cea-01794078 Submitted on 2 Oct 2019 HAL is a multi-disciplinary open access L’archive ouverte pluridisciplinaire HAL, est archive for the deposit and dissemination of sci- destinée au dépôt et à la diffusion de documents entific research documents, whether they are pub- scientifiques de niveau recherche, publiés ou non, lished or not. The documents may come from émanant des établissements d’enseignement et de teaching and research institutions in France or recherche français ou étrangers, des laboratoires abroad, or from public or private research centers. publics ou privés. Distributed under a Creative Commons Attribution| 4.0 International License EPJ Nuclear Sci. Technol. 3, 32 (2017) Nuclear © Sciences J. Guidez and A. Saturnin, published by EDP Sciences, 2017 & Technologies DOI: 10.1051/epjn/2017024 Available online at: https://www.epj-n.org REGULAR ARTICLE Evolution of the collective radiation dose of nuclear reactors from the 2nd through to the 3rd generation and 4th generation sodium-cooled fast reactors Joel Guidez1,* and Anne Saturnin2 1 CEA, DEN, 91191 Gif-sur-Yvette, France 2 CEA, DEN, DMRC, SA2I, 30207 Bagnols-sur-Cèze, France Received: 30 January 2017 / Received in final form: 23 May 2017 / Accepted: 26 September 2017 Abstract. During the operation of a nuclear reactor, the external individual doses received by the personnel are measured and recorded, in conformity with the regulations in force. The sum of these measurements enables an evaluation of the annual collective dose expressed in man·Sv/year. This information is a useful tool when comparing the different design types and reactors. This article discusses the evolution of the collective dose for several types of reactors, mainly based on publications from the NEA and the IAEA. The spread of good practices (optimization of working conditions and of the organization, sharing of lessons learned, etc.) and ongoing improvements in reactor design have meant that over time, the doses of various origins received by the personnel have decreased. In the case of sodium-cooled fast reactors (SFRs), the compilation and summarizing of various documentary resources has enabled them to be situated and compared to other types of reactors of the second and third generations (respectively pressurized water reactors in operation and EPR under construction). From these results, it can be seen that the doses received during the operation of SFR are significantly lower for this type of reactor. 1 Introduction 2 Causes of irradiation during the operation of a reactor Since 1992, the Information System on Occupational Exposure (ISOE) program, supported by the OECD/NEA During reactor operation, several factors contribute to and the IAEA, has collected and analyzed data concerning personnel exposure, with external irradiation due to the radiological exposure of personnel working in nuclear gamma rays being the main contributor. power plants. The electricity producers and national For pressurized water reactors (PWRs), virtually all regulatory authorities of around 30 countries participate the doses absorbed come from the activation of corrosion in this network, which includes 90% of the commercial products coming from the main alloys found in the primary nuclear power reactors in the world (400 operating reactors and auxiliary circuits [3]. More than 90% of the doses and 80 shutdown reactors). Each year, the ISOE draws up absorbed come from surface contamination caused by lists of the collective dose for the different types of reactors activated corrosion products (see Fig. 1). [1,2]. Fission product contamination of the primary circuit Nevertheless, the dose rates for sodium-cooled fast may come from a rupture or from a leak tightness defect in reactors (SFRs), as well as for other facilities in the fuel certain fuel pins. Fission products like krypton, xenon, cycle, have not been assessed by the ISOE program. At iodine or cesium are then released and can be found, Marcoule, the CEA has gathered information published in depending on the case, in gaseous phase or in the coolant. the literature in order to develop a specific database giving In the case of boiling water reactors (BWRs), an additional information. This article is therefore based on additional source of external exposure must be considered these two sources. for personnel working in the turbine hall. This is 16N, an activation product with an energetic gamma ray that is carried by the primary circuit to the turbines. Furthermore radioactive gases, like tritium, may also * e-mail: [email protected] be spread into the circuits. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. 2 J. Guidez and A. Saturnin: EPJ Nuclear Sci. Technol. 3, 32 (2017) Fig. 1. Main contributors to doses coming from surface contamination by activated corrosion products [4]. Fig. 2. Distribution of the French reactor fleet collective doses for shutdown and operational phases [1]. In certain zones of the reactor, the presence of these radionuclides can lead to an increase in the atmospheric radioactivity and may mean temporary access bans when the unit is in operation. During a production period, the personnel exposed to doses are mainly those involved in maintenance operations. The activities causing the highest dose rates usually take place during unit shutdown. According to the ISOE [1]andtheIRSN [5], in PWRs about 80% of the annual radiation exposure can be attributed to maintenance operations carried out during unit shutdown (see Fig. 2). For water-cooled reactors, this may for example include vessel opening operations, equipment handling, maintenance or repair work on contaminated or activated equipment, filter changes, etc. Finally, the balance sheets published show that the dose vary depending on the type of unit shutdown, with the collective dose distribution being, in ascending order: refueling shutdown (“RS”), Fig. 3. Average collective doses for the French reactor fleet by inspections (“I”) or 10-yearly inspections (see Fig. 3). type of unit shutdown [6]. For SFRs, the causes of irradiation during operation are different. For example, activated corrosion products remain confined in the primary circuit and unit shutdown does not mean the vessel or its circuits are opened. J. Guidez and A. Saturnin: EPJ Nuclear Sci. Technol. 3, 32 (2017) 3 man.Sv/year man.Sv/year (LWGR) Fig. 4. Annual collective dose by type of reactor [1]. 3 Collective doses for the main types of reactors (not including SFR) The evolution of annual collective doses for the different types of reactor is shown in Figure 4.Thisfigure, taken from the ISOE report published in 2012, gives average values over three years between 1992 and 2012 for several types, each of the values grouping reactors with different power levels [1]. In spite of these differences, the overall trend observable during recent years, and for all of the reactors taken into account, is a steady decrease in the annual collective dose. The quasi-constant difference between the doses for PWR and BWR reactors can be noted. The PHWR-type (CANDU) reactors are nevertheless the exception, as a slight increase has been noted for them since 1996–1998. This overall trend toward a decrease in the collective dose worldwide is due to several factors, among which are Fig. 5. Average annual collective dose per reactor in the French reinforced regulations, technologicalprogress,improvements fl – in facility design and in water chemistry, in operation eet [10 12]. preparation and procedures,teaminvolvement, and ofcourse data and lessons learned shared at the international scale [7]. Apart from the marked reactor type effect grouping According to the ISOE reports for the period 2010– reactors with different power levels, numerous different 2012, the trends per reactor type [1], independent of their factors may cause the disparities found between different respective power levels, are as follows: countries and sites as concerns exposure to ionizing – a PWR reactor has an average collective dose of radiation. 0.60 man·Sv/year varying between 0.32 and In spite of on-going efforts focusing on good practices, 0.88 man·Sv/year; optimizations, and organization, etc., these figures tend – a BWR reactor has an average collective dose of toward asymptotic values in the different countries. If this 1.12 man·Sv/year varying between 0.43 and trend is confirmed, further decreases can be logically 3.37 man·Sv/year; expected for tomorrow’s reactors through continuing – a CANDU/PHWR reactor has an average collective dose design enhancements. assessed to be around 1.34 man·Sv/year varying between 0.35 and 2.59 man·Sv/year. 4 Evolution of the French PWR fleet The graphite-gas type reactors (gas-cooled reactors, or GCRs), mostly operated in the United Kingdom, give the Like the different reactor fleets elsewhere in the world, the lowest average collective dose, i.e. 0.06 man·Sv/year (note that collective dose for the French reactor fleet has considerably GCRs have a power level of between 475 and 610 MWe [8]). decreased since the 1990s, as a result of progress made in 4 J. Guidez and A. Saturnin: EPJ Nuclear Sci. Technol. 3, 32 (2017) Table 1. Sodium-cooled fast reactors taken into account.